Dive into the rabbit hole on Wikipedia.
The mnemonic major system allows you to translate digits into sounds, which can then be used to create words. I recommend checking out the table on Wikipedia for this (I didn’t think it’d be necessary to copy it here). What’s most important is to remember the mnemonics for each digit-sound/letter-pair.
0 = s, soft c or z, because zero
1 = d or t, they have a vertical stroke, which can represent 1
2 = n, because 2 baseline contacts
3 = m, because 3 baseline contacts
4 = r, because four
5 = l, because Roman L is 50
6 = soft j, g, or ch, because uppercase G looks like 6
7 = k, hard c, g, or ch, because k looks a bit like a 7 when flipped
8 = f or v, because f looks a bit like 8
9 = b or p, because they look a bit like 9
You must remember not only the letters but the respective sounds as well. You can then use those pairs to turn any number into sounds and words, creating a story or visualizations, which are much easier to remember. Helpful tool: Mnemonic Ninja
Personal example: I tested this with decimal digits of pi, as I had tried this before and failed after ~50 digits, remembering roughly 10 after just a few days. My story goes: Darth Jalapeno walks into a dim room and says shalom to Olaf, Habeck, an Obama Nympho, and Russian Jerome. They’re Mafia, Amen. Cap (Captain America) enters the room. They tell him to listen to an idea for Fiverr they had, where they’ll debug Toshiba and maybe IBM machines. They offer Cap a cola, but he declines. He only drinks diesel.
Granted, this story is all over the place. It’s absurd, and it doesn’t make sense right away what words are the keywords and which are not. I know, because this is my own story, and I had to spend a couple of minutes coming up with it. There are also some trippy words, such as “listen” or “Toshiba”. “listen” has an “t” as well, but it’s silent, so I ignored it. This is something I know and will take into consideration, so it works for me. Same with Toshiba. Is the “sh” rather an “s” sound or a “soft ch” sound? I chose the latter because the “sh” has more of a “j” sound than an “s” sound (compare to “Jerome”), making it a 6. For my pi learning, I combined this technique with the memory palace, which is an incredibly powerful combination. This small story alone allows me to recite: 3.141592653589793238462643383297502884197169399375105